Current limit of tps61175

Discussion in 'General Electronics Chat' started by markdem, Feb 3, 2016.

  1. markdem

    Thread Starter Member

    Jul 31, 2013
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    Hi,

    Has anyone used a tps61175 boost converter? I am having a hard time working out how its max output current is worked out.
    The datasheet in section 9.2.2.3 shows how to workout max output current but the calculation needs to know the over current limit. However, it never talks about how it is set..

    The tps61175 is rated at 3A and I need to get 2A at 24V out of it with a 12V 5A input so I think I should be OK.
    I have tried the webbench application but it will not give me a design for 2 A output.

    I have already built a converter and it works fine until I load it with more that about 1A. After that it will just shut down so I am assuming it is the over current limit.

    Can anyone help me understand what I am missing here? What do I need to do to make the output current higher? I have attached my schematic, please ignore the upper part as that works fine.

    Thanks
     
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  2. ronv

    AAC Fanatic!

    Nov 12, 2008
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    @markdem
    Unfortunately the 3 amps is input current and doesn't count in-inefficiencies. So you can't get there.:(
    upload_2016-2-3_18-35-10.png
     
  3. markdem

    Thread Starter Member

    Jul 31, 2013
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    Hmm, that's a downer. I was assuming it was output current.
    Is there anything I could do here to try to squeeze out a few more mA? The measured load maxes out at about 1.4 A and only for a very small amount of time. I just wanted 2A to be on the safe side.

    However, I would like to still know what sets the current limit? (I lim in the calculation.) Or is it just always 3A?

    Thanks again.
     
  4. ronv

    AAC Fanatic!

    Nov 12, 2008
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    It looks like it has 2 current limits. One based on temperature and another based on inductor current.
    http://www.ti.com/lit/ds/symlink/tps61175.pdf
    I suppose for a test you could blow some air on it.
    Could you live with a lower voltage?
     
  5. markdem

    Thread Starter Member

    Jul 31, 2013
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    I was thinking along the lower voltage path. It is driving a BLDC motor so I may have some wriggle room here. I am going to see how I go with a lower switching frequency too.

    Thanks again.
     
  6. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Does it get hot or just shut down?
     
  7. markdem

    Thread Starter Member

    Jul 31, 2013
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    No heat, just shut down. Works fine if I don't load it past ~1A.
     
  8. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Are you sure your inductor is big enough? If it were to saturate that would also do it.
     
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